Equipment used in the microelectronics industry, commonly consists of one or more processing chambers. During the manufacturing process, the silicon wafer is moved through various processing steps and chambers, by use of wafer handling devices such as robots, elevators, indexers, etc. Mechanical stress—scratches, shock or vibration—applied to the wafers during their handling by semiconductor processing machines may generate scratches on one of the surfaces of the wafer, lead to the creation of particles in the processing chamber that interfere with the production process, cause other defects on the surface of the wafer, or may even result in breakage of the wafer.
The scratches or shocks can be caused by bad adjustment of the handling devices or by mechanical parts coming in contact with the wafer or other mechanical parts inside the processing machine during the transfer of the wafer from one position to another within the processing machine. Shocks can also occur when the robot arm picks up the wafer or releases it to or from a docking station. Excessive vibrations during wafer transfer can occur as a result of many types of mechanical problem such as a defective motor or ball-bearing. Shocks and excessive vibrations can also occur when a cassette containing wafers is transferred from one processing machine to another.
Scratches on the front side of the wafer may destroy dies, directly or by impact of particles released from the surface of the wafer. Scratches on the back of the wafer may cause breakage of the wafer or contribute to other malfunctions. For instance, as a result of scratches on the back of the wafer, the wafer may be positioned out of focus during the lithography steps of the manufacturing. The damage may appear long after the defective stage; and, in such a case, it may take extensive efforts to identify the defective machine. Excessive shocks and vibrations may cause similar problems and their causes may be even more difficult to isolate.
The detection and/or measurement of mechanical stress or impact and the determination of its cause are currently difficult and costly. In many cases, the disassembly of the processing machine is required to detect mechanical problems or determine the cause of mechanical problems. This results in conditions that may be very different from those existing during actual operation of the machine. These differences arise for many reasons including, for example, the fact that most machines process wafers under vacuum conditions.
U.S. Pat. Nos. 5,444,637 and 6,140,833 describe devices for monitoring parameters that are important in the manufacturing process such as: temperature, current, voltage, radiation, distance of the wafer surface from masks and other parts of the apparatus, concentration of various gases, etc. These patents describe wafers which have one or more sensors, electronic circuits, and memory devices formed on their surfaces by standard techniques. These wafers are placed in the processing machine and record the relevant data during the operation of the machine. After the process is completed, the data is read from the memory and used to confirm correct operation or suggest adjustments of the measured parameter.
Neither of these or other existing devices or methods, however, is able to provide convenient means for pinpointing the mechanical malfunctions of the processing machine that are the cause of defects in the manufactured wafer.
It is therefore a purpose of this invention to provide a device that can be used to record the motion of a wafer and fine perturbations and vibrations in its motion during its progress through and between semiconductor process and inspection machines in the course of the actual manufacturing process or during a test cycle of the processing or inspection machine.
It is another purpose of this invention to provide a system and a method which uses a record of the motion of a wafer and fine perturbations and vibrations in its motion during its progress through and between semiconductor process machines in the course of the actual manufacturing process or during a test cycle of the processing or inspection machine to detect, locate, and identify any mechanical malfunction of the processing or inspection machine which has caused, or could cause, defects in the manufactured wafer whether directly or indirectly, as for instance, by releasing particles in the processing chamber.
Further purposes and advantages of this invention will appear as the description proceeds.